Tone task proves blind hear better

July 14, 2004By Michael HopkinThis article courtesy of Nature News.

Early vision loss leads to keener hearing.

It is no coincidence that so many
piano-tuners are blind. Folklore says their lack of sight gives them acute
hearing, ideally suited to the task. Now neuroscientists in Canada have shown
that the sightless really do hear notes more precisely if they went blind when
they were very young.

The idea that blindness can aid musical development is an old one, says
Robert Zatorre of McGill University in Montreal, a member of the study team.
Ray Charles and Stevie Wonder, who both lost their sight at an early age, were
among the twentieth century's most influential musicians.

But previous attempts to quantify the effect have met with mixed
results. Zatorre thinks this is because they did not take account of the age at
which subjects went blind.

The researchers therefore divided their 14 blind subjects into two
groups: those who were blind at birth or lost their sight during the first two
years of life, and those for whom blindness came later. The team also tested
fully sighted people to see which of the three groups performed best at
pitch-recognition tasks.

Subjects listened to pairs of tones played one
after the other, and were asked to decide whether the second was higher or
lower than the first. The researchers varied both the difference in pitch of
the two tones and their duration.

Note perfect

‘Early blind’ subjects outperformed the other groups in every way,
continuing to make correct distinctions as the notes got either shorter or
closer in pitch. In fact, as the team reports in this week's Nature1, early-blind participants performed as well on the most rapid notes
as sighted subjects did on notes ten times longer.

The blind subjects’ ages ranged from 21 to 46, the researchers add. This
shows that it is the age at which blindness occurs, rather than simply the
number of years spent without vision, that determines sensitivity to
pitch.

“In normal brains these connections are gradually
eliminated. But in the early blind they might be preserved and
used.”

Pascal BelinUniversity of Montreal

The discovery reveals a lot about the brain's capacity to reorganize
itself early in life, says study leader Pascal Belin of the University of
Montreal. He suspects that the visual cortex, the part of the brain that
usually deals with vision, can be used to process other sensory information if
given the chance.

At birth, the brain's centres for vision, hearing and other senses are
all connected, Belin says. "In normal brains these connections are gradually
eliminated. But in the early blind they might be preserved and used."

That would allow regions such as the visual cortex to help with the job
of processing sounds. But, as the new research shows, there comes a point after
which is too late for the brain to adapt.

When all the senses are intact, the brain does not need lots of
connections between sensory centres; the amount of information buzzing around
would be too confusing, says Zatorre. "It's like pruning a tree, you only keep
the branches that get more light," he says. But when your world is shrouded in
darkness, a little extra brain power can be a big help.